A single HTTP call may require follow-up requests to be made to handle authentication challenges, redirects, and HTTP-layer timeouts. In such cases multiple connections, requests, and responses may be attempted. Follow-ups are another reason a single call may trigger multiple events of the same type.

![Events Diagram](../assets/images/******@****.***)

The simplest FastAPI file could look like this:

{* ../../docs_src/first_steps/tutorial001_py39.py *}

Copy that to a file `main.py`.

Run the live server:

<div class="termy">

```console
$ <font color="#4E9A06">fastapi</font> dev <u style="text-decoration-style:solid">main.py</u>

  <span style="background-color:#009485"><font color="#D3D7CF"> FastAPI </font></span>  Starting development server 🚀

In this scenario of "fast food burgers with your crush", as there is a lot of waiting 🕙, it makes a lot more sense to have a concurrent system ⏸🔀⏯.

This is the case for most of the web applications.

Many, many users, but your server is waiting 🕙 for their not-so-good connection to send their requests.

And then waiting 🕙 again for the responses to come back.

# Behind a Proxy { #behind-a-proxy }

In many situations, you would use a **proxy** like Traefik or Nginx in front of your FastAPI app.

These proxies could handle HTTPS certificates and other things.

## Proxy Forwarded Headers { #proxy-forwarded-headers }

import pytest
from dirty_equals import IsInt
from fastapi.testclient import TestClient
from inline_snapshot import Is, snapshot
from sqlalchemy import StaticPool
from sqlmodel import SQLModel, create_engine
from sqlmodel.main import default_registry

from tests.utils import needs_py310


def clear_sqlmodel():
    # Clear the tables in the metadata for the default base model
    SQLModel.metadata.clear()

The same way, you can define logic (code) that should be executed when the application is **shutting down**. In this case, this code will be executed **once**, **after** having handled possibly **many requests**.

This would allow you to have a more fine-grained permission system, following the OAuth2 standard, integrated into your OpenAPI application (and the API docs).

OAuth2 with scopes is the mechanism used by many big authentication providers, like Facebook, Google, GitHub, Microsoft, X (Twitter), etc. They use it to provide specific permissions to users and applications.

              files=".*[/\\]stdlib-java-extensions[/\\]src[/\\]main[/\\]java[/\\]org[/\\]gradle[/\\]api[/\\][^/\\]+"/>
    <suppress checks="JavadocPackage"
              files=".*[/\\]model-core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]gradle[/\\]api[/\\][^/\\]+"/>
    <suppress checks="JavadocPackage"
              files=".*[/\\]core[/\\]src[/\\]main[/\\]java[/\\]org[/\\]gradle[/\\]api[/\\][^/\\]+"/>
    <suppress checks="JavadocPackage"

/target/
/work/
/bin/
/mydbflute/
/solr/data/
/src/main/webapp/WEB-INF/classes/
/src/main/webapp/WEB-INF/lib/
/src/main/webapp/WEB-INF/site/
/src/main/webapp/WEB-INF/plugin/*
!/src/main/webapp/WEB-INF/plugin/.keep
/src/main/webapp/WEB-INF/env/crawler/lib/
/src/main/webapp/WEB-INF/env/suggest/lib/
/src/main/webapp/WEB-INF/env/thumbnail/lib/
/src/main/webapp/WEB-INF/thumbnails/
/src/main/webapp/jar/
/dbflute_fess/extlib/*

RUN pip install --no-cache-dir --upgrade -r /code/requirements.txt

# (1)!
COPY ./main.py /code/

# (2)!
CMD ["fastapi", "run", "main.py", "--port", "80"]
```

1. Kopiere die Datei `main.py` direkt in das Verzeichnis `/code` (ohne ein Verzeichnis `./app`).

2. Verwenden Sie `fastapi run`, um Ihre Anwendung in der einzelnen Datei `main.py` bereitzustellen.